The measurement of systolic, diastolic, and mean blood pressure values by measuring cuff pressure oscillations caused by patient blood vessel pulses during deflation of the cuff is a known technique. Oscillometric blood pressure measurement is taken at numerous anatomical sites in the body including the upper arm, forearm, wrist, finger, ankle, calf and thigh. These sites are roughly cylindrical in shape and easily lend themselves to placement of a wrap-around rectangular inflatable cuff to intermittently restrict blood flow.
At cuff pressures above systolic pressure, minimal blood flow occurs and no pressure oscillations are received in a monitoring device. As cuff pressure is decreased, blood vessel oscillations are sensed in the monitoring device and the amplitude of these oscillations becomes larger. The cuff pressure at which oscillations are largest is typically considered to correlate with mean pressure. As pressure in the cuff is decreased further, oscillations become smaller and eventually are no longer present. Mean, systolic and diastolic pressures are sensed and determined by computer analysis in the monitoring device of the changes in the oscillation amplitudes during cuff deflation as is known in the art.
Traditional methods of oscillometrically measuring BP on the arm with a rectangular pressure cuff has several disadvantages. Firstly, the upper arm, the most commonly used site, is difficult to use if the patient is obese, or if the arm is conically shaped. Secondly, the use of the upper arm and other sites that include a substantial amount of soft issue, particularly fat and muscle, tend to be associated with more patient discomfort. Thirdly, measurement of BP in the arm or forearm is contra-indicated in some patients, such as those who have undergone mastectomy surgery with lymph node dissections, and patients with renal dialysis grafts in their arms. Though this restriction is typically limited to only one arm, these patients often have other devices and intravenous catheters placed on the opposite arm, and the measurement of BP via the arm typically interferes with the function of these devices. Finally, the upper arm is prone to artifacts during surgical procedures because patients arms are often tucked in at their sides during surgery. If a surgeon should happen to lean against a patient while operating on the upper abdomen or chest, the BP monitor may have difficulty separating BP oscillations from random oscillations generated by external pressure applied to the cuff by the surgeon. Traditional rectangular arm cuffs are difficult to use by an individual without assistance, because two hands are typically required to attach and use the cuff. Finger BP measurements are prone to error because of peripheral vaso-constriction, which is a common occurrence in the digits.
It would be desirable to provide a practical and readily usable method and apparatus to measure blood pressure which does not employ the traditional rectangular blood pressure cuff.